In my opinion, Froakie's final stage will be Water/Dark. I believe that the starters will form the second "trio" (Fighting/Psychic/Dark), but Chespin doesn't look appropriate for the "Dark" role, it is shown always happy... Froakie however was shown launching foam-shuriken, assuming ninja-pose, and using his foam like a sort of a balaclava/mask; it has also ninja abilities like high-jumping, and it is shown always serious and concentrated. Those are all ninja-traits, and a ninja is the exact contrary of a samurai (which is a rightful warrior), it's a mean and dishonest fighter, a dirty player, and that's exactly what the Dark type represents. Fighting type represents Dark opposite, a fair fighter, and a ninja can't be Fighting type. So if the "Dark/Psychic/Fighting" trio is true Froakie will be Water/Dark, and Chespin, which is a loyal and happy pokémon, will be Grass/Fighting.
